Chelsea used to trot out in Champions League quarter-finals with a swagger, their aspirations to claim this club's first European Cup very realistic. Their qualities were so persuasive that it seemed only a matter of time before the trophy, like the Premier League, would be theirs. So it says much about the steady erosion of power that, with Benfica awaiting at the Estádio da Luz on Tuesday evening, the standout quote delivered in the buildup addressed frailty rather than fortitude. Times have changed.

It was Frank Lampard, on Chelsea's in-house television channel, who delivered the simple if brutally honest assessment of a campaign that has already cost the club one manager and could yet deny them participation in this competition for the first time under Roman Abramovich's ownership. The England midfielder was addressing the side's league position rather than their prospects against the Portuguese when he admitted: "We're not as good as we used to be. Chelsea should be in the top four. No disrespect to the other top five clubs but, with the ability we have, we should be in there."

There were attempts of sorts to offer a more upbeat assessment, suggestions that the five-point gap from fourth "has been bigger than that" and that it was "far from over", but the tone had been set. The local media in Lisbon has made much in recent days of footage, again on Chelsea TV, that appeared to show Didier Drogba celebrating with a mock "quaking in his boots" routine as the quarter-final draw played out on television back at the club's Cobham training base.

Chelsea insist the clip has been taken out of context, though the reality is Benfica would have been just as relieved to draw the Premier League club once Apoel Nicosia and Marseille had been paired elsewhere.

The Portuguese are unbeaten in 10 European home games and have lost only once here, to Porto, all season. Chelsea, in contrast, have won only once away from home in Europe since October 2010 – and that at FC Copenhagen, who were in the midst of their winter break – and led only to be pegged back in all of their Champions League trips this term. Valencia and Genk claimed a point. The comebacks mounted by Bayer Leverkusen and Napoli yielded victories, with the London club's progress to this point effectively carried by immaculate home form.

Some greater solidity on their travels will be required on Tuesday night; the competition's better teams, of which Benfica are one, will surely not prove quite so accommodating when visiting west London from now on in.

The hope will be that rare underdog status might bring the best out of the visitors. Chelsea are newcomers here but Roberto Di Matteo, a stand-in manager whose contract has entered its final four months, has spoken with his compatriot Luciano Spalletti at Zenit St Petersburg, eliminated by Benfica in the previous round, to glean an insight into the threat that awaits. He will surely also have tapped into André Villas-Boas's knowledge, for all that the manager is still coming to terms with his abrupt dismissal this month.

The interim first-team coach acknowledged Lampard's honesty, but retains confidence in his charges. "We've had a difficult season – the numbers say that – so there is no point denying it," he said. "But I still think this Chelsea team is a very good team. Sure, we are used to being in the top two or three, at least, so it's been hard for us, domestically. But we can still recover. There are still eight games. We've been playing catchup from day one. That's the reality. But football has taught me that nothing is ever as straightforward as you think. People might expect the other teams to win all their games but they might not.

"And we are in the quarter-finals of the Champions League and the semi-finals of a domestic cup. I have faith in this team. They've shown, against Napoli, they can play at high intensity. Things looked a little gloomier two weeks ago, so we're pleased to be here and I am positive. From the conversations I've had with my players, they're positive too."

They arrive with reputations forged by five semi-final appearances in six years, albeit the last of which having come in 2009, but aware of Benfica's qualities. The Portuguese topped United's group before Christmas and, in the prolific Oscar Cardozo and the precociously talented Nicolás Gaitán, a player attracting interest from Manchester United and Manchester City, boast the ability to prise Chelsea apart even if they are hampered by their own defensive frailties. The visitors may start with Fernando Torres rather than Drogba in the hope that slippery counterattacking may secure reward.

Not since 1990 have Benfica reached the last four of this competition and, even if he does not start, that video of Drogba has clearly struck a nerve. "Who knows what he was thinking? He might just have been joking, we don't know," said the coach, Jorge Jesus. "But Portuguese clubs have eliminated both Manchester United and Manchester City, the top two teams in the Premier League, from Europe this season so that should act as an indication of the strengths of Portuguese football. Any response to Didier Drogba we'll give out on the field." A testing occasion awaits.